Recently, in order to improve resource exhaustion and environmental issues, various methods for increasing the efficiency of an electric apparatus have been spotlighted.
In an illumination field, an existing illumination apparatus using a fluorescent lamp or a mercury lamp has been replaced with an LED lamp due to energy inefficiency. The LED lamp is required to have a high power factor in order to increase the energy efficiency.
A conventional AC-DC converter for driving an LED lamp may have a two-stage structure employing a boost converter and a flyback converter in order to obtain a high power factor. The boost converter is provided for power factor correction and the flyback converter is provided for DC-DC converting.
The AC-DC converter having the aforementioned two-stage structure requires an active element and a control loop according to steps. That is, the aforementioned AC-DC converter is required to use a large number of circuit elements due to the two-stage structure. Therefore, the AC-DC converter having the aforementioned two-stage structure is not suitable for low power applications such as indoor electric lights in terms of design or cost.
In order to solve the aforementioned problems, the use of an AC-DC converter having a single-stage structure employing a link capacitor may be proposed. In the AC-DC converter of the single-stage structure, one controller may be provided and the number of required circuit elements may be reduced. In this regard, it may be recommended to apply the AC-DC converter of the aforementioned single-stage structure to low power applications such as indoor electric lights.
However, in the AC-DC converter of the aforementioned single-stage structure, capability for reducing ripples of an input voltage is lower than that of the AC-DC converter of the two-stage structure. Therefore, when the conventional AC-DC converter of the aforementioned single-stage structure is applied to low power applications in order to drive an LED lamp, there is a problem that flicker occurs and color change is caused.
The aforementioned problems of the conventional AC-DC converter of the single-stage structure may be solved using a link capacitor having large capacitance. However, when the capacitor has large capacitance, the size of the capacitor increases. Therefore, it is not preferable to configure an AC-DC converter by employing a capacitor having a large size in order to realize low power applications.
Furthermore, for an AC-DC converter to be employed for low power applications, a method capable of reducing ripples of an output current should be considered.